1. Field of the Invention
The present invention relates to an optical system and more specifically to a zoom lens suitable for use in an image pickup apparatus such as electrophotographic cameras and video cameras.
2. Description of the Related Art
Zoom lenses for image pickup apparatuses that use solid-state image pickup elements, such as digital cameras and video cameras, are required to have a compact optical system having a high zoom ratio. A known example of zoom lenses that satisfy those requirements is a positive-lead type zoom lens in which a lens unit closest to the object to be imaged is constituted of lenses having positive refractive power. Another known zoom lens has image stabilizing function involving compensating image blur that occurs when vibrations propagate to an image capturing system by moving some of the lens units in a direction perpendicular to the optical axis. A known example of the positive-lead type zoom lens is a compact zoom lens having a high zoom ratio and image stabilizing function, composed of lens units having, in order from the object side to the image side, positive, negative, positive, negative, and positive refractive power. U.S. Pat. Nos. 7,609,446 and 7,428,107 disclose zoom lenses having image stabilizing function in which image blur is corrected by moving a fourth lens unit in a direction perpendicular to the optical axis. Another known example of the positive-lead type zoom lens is described in U.S. Pat. No. 7,206,137. U.S. Pat. No. 7,206,137 discloses a zoom lens constituted of, in order from the object side to the image side, five lens units having positive, negative, positive, positive, and positive refractive power. As used herein, the side of a lens where an object to be imaged is placed is referred to as the object side or front side of the lens; and the side of the lens where the image is formed is referred to as the image side or back side of the lens.
To correct image blur (motion blur) by moving a compensation lens unit in the direction perpendicular to the optical axis, the compensation lens unit is required to be small and lightweight to achieve the size reduction and power saving of a moving mechanism. In addition, minimal aberration changes during image blur correction and high optical performance are also required. To obtain a zoom lens that satisfies those requirements, it is important to appropriately set the zoom type and the configuration of the image stabilizing compensation lens unit.